Hyperpolarized 13C magnetic resonance metabolic imaging: application to brain tumors

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Abstract
In order to compare in vivo metabolism between malignant gliomas and normal brain, C-13 magnetic resonance (MR) spectroscopic imaging data were acquired from rats with human glioblastoma xenografts (U-251 MG and U-87 MG) and normal rats, following injection of hyperpolarized [1-C-13]-pyruvate. The median signal-to-noise ratio (SNR) of lactate, pyruvate, and total observed carbon-13 resonances, as well as their relative ratios, were calculated from voxcls containing Gadolinium-enhanced tissue in T-1 postcontrast images for rats with tumors and from normal brain tissue for control rats. [1-C-13]-labeled pyruvate and its metabolic product, [1-C-13]-lactate, demonstrated significantly higher SNR in the tumor compared with normal brain tissue. Statistical tests showed significant differences in all parameters (P<.0004) between the malignant glioma tissue and normal brain. The SNR of lactate, pyruvate, and total carbon was observed to be different between the U-251 MG and U-87 MG models, which is consistent with inherent differences in the molecular characteristics of these tumors. These results suggest that hyperpolarized MR metabolic imaging may be valuable for assessing prognosis and monitoring response to therapy for patients with brain tumors.